Supercondenzadores a partír de materiales carbonosos para almacenamiento de energía

En esta tesis se prepararon y caracterizaron diferentes materiales de carbono para ser usados como electrodos de supercondensadores. Los supercondensadores son un tipo de condensador eléctrico con una capacidad eléctrica muy superior a cualquier otro tipo de condensador. En su constitución básica, están formados por dos electrodos (separados por un aislante eléctrico) y un electrolito iónico. Los desafíos actuales en el desarrollo de supercondensadores se focalizan en aumentar la densidad de energía del dispositivo. Por el lado de los materiales de electrodo, esto se puede lograr con el desarrollo de materiales que tengan una elevada capacidad eléctrica específica. El trabajo experimental de esta tesis se focalizó en la preparación y caracterización de carbones en polvo activados, y monolitos de carbón obtenidos a partir de diferentes cortes (longitudinal al eje de crecimiento del tronco del árbol y transversal al eje del tronco) de madera Eucaliptus Grandis. Los materiales fueron preparados mediantes diferentes métodos y condiciones de activación (generación de porosidad) y fueron caracterizados mediante análisis textural, análisis elemental, Desorción Térmica Programada (TPD), difracción de rayos X (DRX), microscopía electrónica de barrido (SEM), medidas de conductividad eléctrica y electroquímicas. Las caracterizaciones electroquímicas (curvas galvanostáticas de carga y descarga, voltametría cíclica e impedancia electroquímica) se llevaron a cabo utilizando una celda de laboratorio simétrica tipo Swagelok usando dos tipos de electrolitos: (i) solución acuosa H2SO4 2M (electrolito ácido) y (ii) Et4NBF4 disuelto en acetonitrilo 1M (electrolito orgánico). IV Los resultados obtenidos para los carbones en polvo indican que estos tienen áreas superficiales que varían en un amplio rango dependiendo del método y condiciones de preparación. De acuerdo con los resultados del TPD, el contenido de grupos funcionales oxigenados superficiales de los carbones varía también según el método y condiciones de preparación. La conductividad eléctrica de los materiales depende marcadamente de la temperatura máxima de preparación siendo prácticamente independiente del método o agente activante utilizado. Se determinó la existencia de una correlación directa de la capacidad eléctrica específica de los materiales con el área superficial y el contenido de grupos funcionales oxigenados superficiales determinados mediante TPD. Los mejores resultados en cuanto a capacidad eléctrica específica en electrolito ácido se determinó para el carbón activado con ZnCl2 a 900 C seguido de una posterior oxidación con ácido nítrico. Se comprobó que la energía acumulada para un mismo carbón es mayor en el electrolito orgánico que en el electrolito ácido. El análisis de los monolitos demuestra que existe una incidencia directa de la anisotropía de la madera en las propiedades texturales, eléctricas y electroquímicas de los monolitos de carbón obtenidos. Los monolitos obtenidos a partir del corte transversal presentaron una estructura más abierta con mayor desarrollo de porosidad (la más alta obtenida para los activados con CO2), mayor capacidad eléctrica específica gravimétrica, mayor energía gravimétrica y mayor conductividad eléctrica. Sin embargo no se encontraron diferencias sustanciales en la capacidad y energía volumétrica para los dos tipos de monolitos estudiados. Los mejores resultados de capacidad eléctrica y energía acumulada obtenidos para los materiales de carbón preparados en esta tesis fueron mejores a los obtenidos para un carbón comercial de referencia y otros materiales similares reportados en la bibliografía

Microporus activated carbon fiber felt from Brazilian textile PAN fiber: preparation, characterization and application as super capacitor electrode

Activated carbon fibers (ACF) are known as excellent adsorbent materials due to their fast adsorption rate and easy handling characteristic. The ACF can be manufactured from the polyacrylonitrile fiber, based on an usual carbon fibers (CF) production process accomplished by an additional activation process. The aim of the present work is to describe the production, chemical/morphological characterization and application potentiality of activated carbon fiber felt (ACFF) produced from textile PAN fiber, using a set of homemade equipment. The 5.0 dtex PAN fiber tow with 200 thousand filaments was oxidized and used as raw material for felt production. The oxidized PAN fiber felt (OPFF) was displaced in a special sample holder, carbonized (900 °C) and then activated in CO2 atmosphere at 1000 °C in an electric tubular furnace. All steps of the process were performed as fast as possible, and characterization was done by 77 K N2 isotherms, adsorption isotherms in liquid phase, scanning electronic microscope, X-ray diffraction and surface chemistry by Bhoem methodology. The results confirmed the production of essentially microporous (pore < 3.2 nm, centered on 1.2 nm) and 1,300 m2 g-1 surface area. The ACFF produced have demonstrated a strong potential application as electrode supercapacitor

Process of converting human hair into hollow carbon filament for electrochemical capacitor

Carbon material is the largest material used as electrode on advanced energy storage devices. The modern lifestyle requires more energy, consequently, more smart energy use and efficient devices are needed. The constant evolution of materials technologies looking for green material and renewable raw material, that have minimal impact on the environment, is one of the most important subjects studied in recent years.  The scientific and industry community are paying more attention to new forms of carbon such as nanotubes, graphene, and activated carbon fiber. The purpose of this work is to convert human hair into a hollow carbon filament to be used as a supercapacitor electrode. The human hair needs 3 stages to be converted into carbon filament: textile manufacture, oxidation, and carbonization. The electrochemical behavior was analyzed in a threeelectrode electrochemical cell system with 2 M of H2SO4 electrolyte medium. The behavior of the electrode was characterized electrochemically by galvanostatic charge/discharge curves, cyclic voltammetry, and electrochemical impedance spectroscopy, showing 163 F g-1 of a maximum value of specific capacitance.Keywords: Residue. Human hair. Felt. Carbon filament. Supercapacitor.

The conversion of wood residues, using pilot-scale technologies, into porous activated biochars for supercapacitors

In this study, activated biochar was produced using pilot-scale technologies of fast pyrolysis and activation to create desirable morphology, surface chemistry, and adsorptive properties for application in supercapacitors. First, residues from white birch were converted into biochar by fast pyrolysis (~ 450 °C). Then, physical (using CO2) or chemical (using KOH) activation was carried out in a homemade pilot-scale furnace at 900 °C. These synthesized materials presented distinct porosity structures: micro-/mesoporous (CO2 material) and highly microporous (KOH material), reaching surface areas of up to 1700 m2 g−1. Electrochemical results showed that KOH-activated biochar had higher specific electrical capacitance in both acidic and neutral electrolytes with a maximum specific capacitance value of 350 and 118 F g−1 at 1 A g−1, respectively; while, for CO2-activated biochar, the maximum obtained values were 204 and 14 F g−1. The greater proportion of oxygenated and nitrogenated functional groups on the surface of the KOH activated biochar, along with its high surface area (with wider porosity), improved its performance as a supercapacitor electrode. Specifically, the low proportion of ultramicropores was determinant for its better electrochemical behavior, especially in the neutral electrolyte. Indeed, these results are similar to those found in the literature on the electrical capacitance of carbonaceous materials synthesized in a small-scale furnace. Thus, the chemical-activated biochar made from wood residues in pilot-scale furnaces is a promising material for use as electrodes for supercapacitors

E. grandis as a biocarbons precursor for supercapacitor electrode application

Wood residues are ordinary wastes in the forestry industry and their valorization is an important issue. Eucalyptus grandis wood dust was chosen as a model wood residue and biocarbons (BCs) and activated BCs were prepared from it and studied as active materials for supercapacitor electrodes. Several ordinary activation methods were used and microporous activated BCs with specific surface areas up to 900 m2 g-1, and different content of oxygenated surface groups were obtained. The preparation or activation temperature is the parameter that mainly affects the electrical conductivity. For temperatures above 700 °C, the samples reach an electrical conductivity as high as 1 S cm-1. The specific capacitance of the activated BCs reaches values up to 203 F g-1 in acidic electrolyte. The highest specific capacitance is obtained when chemical activation with ZnCl2 at 900 °C followed by chemical oxidation with nitric acid is used. BCs activated with ZnCl2 at 900 °C and CO2 at 800 °C displayed good rate capability and the maximum power density. Activation with ZnCl2 at 900 °C also leads to BCs with the maximum energy density. These results show that E. grandis wood dust is a promising low cost and environmental friendly precursor for biocarbon electrodes. © Springer Science+Business Media Dordrecht 2013.Financial support from the projects (MAT 2011-25198 and ANII PR_FSE_2009_1_09) is gratefully acknowledged. V. Barranco thanks the Spanish MINECO for R&C contract.Peer Reviewe

Co-combustion behaviours of a low calorific Uruguayan Oil Shale with biomass wastes

In the present work thermal transport properties, thermochemical characteristics and gaseous pollutants released during co-combustion of different biomasses with oil shales (OS) were assessed using three different mass ratios (25%, 50% and 75% OS-biomass). The biomasses selected for carrying out the analysis were grape pomace (GP), rice husk (RH) and eucalyptus grandis (EG). In this sense, we demonstrated that the addition of biomass to the OS turns out having a positive effect, it improves the combustion index and diminishes the amount of pollutant emissions per energy unit released. Cone calorimeter tests were carried out in order to determine the effective heat of combustion (EHC) and subsequently the energetic combustion efficiency (EHC/HHV) taking as reference the higher heating value (HHV). The higher thermal diffusivity value was obtained for EG (0.161 mm/s) and the lowest value was obtained for GP (0.105 mm/s). The EHC/HHV ratio was obtained for a blending proportion of 50% for OS-EG (0.88–0.98). According to combustion index results, blends containing c.a 50% OS-EG reached a good burning performance of the combustion process, providing a potential OS-biomass ratio for being used as fuel. Moreover, the co-combustion emissions per energy unit released were analysed by means of TG-FTIR. CO, CO and SO patterns showed that the emissions diminished with the addition of biomass to the OS. This paper aims to perform an assessment of the potential utilization of OS-biomass blends based on the biomass and OS composition, their thermal properties, gas emissions per energy unit released and EHC/HHV ratio

Biocarbon monoliths as supercapacitor electrodes: Influence of wood anisotropy on their electrical and electrochemical properties

All rights reserved. Biocarbon monoliths were obtained from Eucalyptus grandis and the influence of wood anisotropy on the electrical and electrochemical performance as supercapacitor electrodes was studied. They were produced from wood pieces cut along the transversal and longitudinal direction of the tree trunk, followed by pyrolysis and, for some of them, also by activation with CO2. Monoliths with drilled channels were also obtained. All the monoliths were characterized by SEM, nitrogen adsorption/desorption isotherms, electrical conductivity measurements and electrochemical measurements, the latter in 2M aqueous H2SO4 electrolyte. Electrical conductivity and specific capacitance are higher for the transversal carbon monoliths than for the longitudinal ones. The electrical conductivity reaches values up to 27 S cm-1 for the transversal monolith. The specific capacitance reaches values up to 260 F g-1for the transversal monolith that was activated and drilled. However, the highest volumetric capacitance, of 90 F cm-3, is found for the longitudinal monolith that was activated and non-drilled. The energy density and power density, both referred to gravimetric and volumetric magnitudes, reach values as high as 36 Wh kg-1 and 12 Wh L-1, and 2181 W kg-1 and 783 W L-1, respectively. Comparison with a commercial powder activated carbon is provided

Supercapacitor Electrode Based on Activated Carbon Wool Felt

An electrical double-layer capacitor (EDLC) is based on the physical adsorption/desorption of electrolyte ions onto the surface of electrodes. Due to its high surface area and other properties, such as electrochemical stability and high electrical conductivity, carbon materials are the most widely used materials for EDLC electrodes. In this work, we study an activated carbon felt obtained from sheep wool felt (ACF&rsquo;f) as a supercapacitor electrode. The ACF&rsquo;f was characterized by elemental analysis, scanning electron microscopy (SEM), textural analysis, and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the ACF&rsquo;f was tested in a two-electrode Swagelok&reg;-type, using acidic and basic aqueous electrolytes. At low current densities, the maximum specific capacitance determined from the charge-discharge curves were 163 F&middot;g&minus;1 and 152 F&middot;g&minus;1, in acidic and basic electrolytes, respectively. The capacitance retention at higher current densities was better in acidic electrolyte while, for both electrolytes, the voltammogram of the sample presents a typical capacitive behaviour, being in accordance with the electrochemical results

Clean synthesis of biocarbon-supported Ni@Pd core–shell particles via hydrothermal method for direct ethanol fuel cell anode application

Direct ethanol fuel cells (DEFCs) are devices for clean and sustainable energy production, where the generation of electrical energy occurs as a result of the anodic ethanol oxidation reaction (EOR). One of the main challenges of these devices is the development of cost-efective and sustainable anodic catalysts, minimizing the use of noble metals such as Pd. In this sense, biomass-derived carbon-supported core–shell nanoparticles of PdNi-based electrocatalyst are of great interest for EOR and its application in DEFCs. The purpose of this work was to demonstrate the possibility of synthesizing a core–shell Ni@Pd electrocatalysts via hydrothermal method, in a fast, simple and environmental friendly way. A biomass hydrothermal liquefaction method using nickel and palladium salts was used to synthesize a biocarbon-supported nickel/palladium core–shell electrocatalyst (Ni@Pd/aHC). The electrocatalyst was morphological and chemical characterized in order to confrm the core–shell particle formation. The electrochemical characterization showed that the Ni@Pd/aHC sample has good electrocatalytic behaviour and good stability over time. The EOR mechanism on the sample and their infuence in the faradaic efciency of a cell were also studied by spectroelectrochemical analysis

Phosphorus/Sulfur-Enriched Reduced Graphene Oxide Papers Obtained from Recycled Graphite: Solid-State NMR Characterization and Electrochemical Performance for Energy Storage

The reduction of graphene oxide (GO) by means of thermal and/or chemical treatments leads to the production of reduced graphene oxide (rGO)—a material with improved electrical conductivity and considered a viable and low-cost alternative to pure graphene in several applications, including the production of supercapacitor electrodes. In the present work, GO was prepared by the oxidation of graphite recycled from spent Li-ion batteries using mixtures of sulfuric and phosphoric acids (with different H2SO4/H3PO4 ratios), leading to the production of materials with significant S and P contents. These materials were then thermally reduced, resulting in rGO papers that were investigated by solid-state 13C and 31P nuclear magnetic resonance, along with other methods. The electrochemical properties of the produced rGO papers were evaluated, including the recording of cyclic voltammetry and galvanostatic charge–discharge curves, besides electrochemical impedance spectroscopy analyses. The samples obtained by thermal reduction at 150 °C exhibited good rate capability at high current density and high capacitance retention after a large number of charge–discharge cycles. The results evidenced a strong relationship between the electrochemical properties of the produced materials and their chemical and structural features, especially for the samples containing both S and P elements. The methods described in this work represent, then, a facile and low-cost alternative for the production of rGO papers using graphite recycled from spent batteries, with promising applications as supercapacitor electrodes